Abstract:
It is found that samples of manganites La$_{0.9}$Sr$_{0.1}$MnO$_3$ (single crystal), Eu$_{0.7}$A$_{0.3}$MnO$_3$ (A = Ca, Sr) (ceramics) and La$_{0.1}$Pr$_{0.6}$Ca$_3$MnO$_3$ and La$_{0.84}$Sr$_{0.16}$MnO$_3$ (thin epitaxial films) that are either field-cooled (in a magnetic field) or zero-field-cooled differ in low-temperature magnetization, and the hysteresis loop of field-cooled samples exhibits a displacement. This displacement signifies that a ferro-antiferromagnetic state occurs in these samples. The exchange integral $J\sim 10^{-6}\,$eV is calculated from this displacement, which describes the exchange Mn-O-Mn coupling through the interface ferromagnetic droplet-antiferromagnetic matrix. The magnetoresistance and volume magnetostriction of La$_{1-x}$Sr$_x$MnO$_3$ single crystals exhibit similar dependences on $x$, temperature, and the magnetic field in the vicinity of the Curie point, which points to the fact that these dependences are due to the same reason, namely, the occurrence of a magnetic two-phase ferro-antiferromagnetic state caused by strong $s-d$ exchange.
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